1. Field of the Invention
The present invention relates to an endoscope signal processor, endoscope apparatus and endoscope signal processing method in which signal processing adaptable even to an endoscope incorporating a high-pixel image pickup device is performed.
2. Description of the Related Art
In recent years, endoscopes incorporating image pickup devices have been put to wide use, for example, in the medical field. There are various kinds of endoscopes having insert portions of different lengths according to portions on which endoscopic inspections are to be performed or the like. For example, in such endoscopes, the length of a cable from an image pickup device to a signal processor for performing signal processing on the image pickup device to generate an endoscopic image varies.
If the cable length varies as described above, the amount of delay of transmission of a drive signal in the case of driving the image pickup device by the drive signal varies. The actual timing of input of an output signal output from the image pickup device to the signal processor also varies.
There is, therefore, a need to perform an adjustment operation for suitably setting, according to the amount of delay by the cable length, the timing of generation of sampling pulses for extracting actual signal components in the output signal from the image pickup device.
For example, Japanese Patent Laid-Open No. 6-86138 discloses a signal processor using a phase-locked loop circuit (PLL circuit) for enabling such an adjustment operation to be automatically performed.
In this disclosed related art, a signal is obtained by photoelectric conversion in an image pickup device having predetermined numbers of pixels arranged in horizontal and vertical directions, which photoelectric conversion is performed by applying a drive signal to the image pickup device. Readout of the signal from the image pickup device is performed as described below.
That is, this signal processor generates a gate signal in each of intermittent periods defined by setting as a phase adjustment period an empty-pixel period in which no pixels exist in each horizontal readout period, and sets the PLL circuit in an operable state to generate a timing signal phase-synchronized with reset pulses (as a reference clock) output from the image pickup device.